Public health experts are warning that more effort needs to be made to alert people in the developing world to the dangers of smoking tobacco.

A Canadian study of 27,000 people has showed exposure to any form of tobacco - including chewing and "bubble" pipes - boosts heart attack risk.

There are estimated to be 1.3bn smokers worldwide, 82% of whom live in developing countries.

Heart experts said the Lancet study was further evidence smokers should quit.

This study provides further evidence that tobacco exposure - whether it be smoking, chewing or inhaling - is seriously bad news for your heart health

Ruairi O'Connor, British Heart Foundation

Most research has looked at people in developed countries who smoke cigarettes.

This study looked also looked at chewing tobacco, smoking 'bubble pipes' or sheesha smoking (where tobacco is smoked through a water pipe) which is common in the Middle East and beedie smoking - where tobacco is rolled in a dried leaf and tied with a string, popular in South Asia.

The researchers, from McMaster University in Ontario, looked at 12,400 heart attack patients in 52 countries and compared them with 14,000 healthy people.

They concluded that, overall, heart attack risk was increased three-fold in smokers compared with people who had never smoked.

Passive smoking

Chewing tobacco doubled the chances of having a heart attack, as did smoking eight to 10 cigarettes a day.

Heart attack risk decreased with time after people stopped smoking.

In the case of light smokers who had fewer than 10 cigarettes a day, there was no excess risk three to five years after quitting.

However, people who smoked 20 or more cigarettes a day still had a 22% increased risk 20 years after giving up.

The study also concluded second-hand smoke was dangerous to the heart.

The team found people exposed to passive smoking for at least 22 hours a week increased their risk of a heart attack by around 45%.

Professor Salim Yusuf from McMaster University in Ontario, Canada, who led the study, said: "Since the risks of heart attack associated with smoking dissipate substantially after smoking cessation, public health efforts to prevent people from starting the habit and promote quitting in current smokers, will have a large impact in the prevention of heart attacks worldwide."

Ruairi O'Connor, of the British Heart Foundation, said: "This study provides further evidence that tobacco exposure - whether it be smoking, chewing or inhaling - is seriously bad news for your heart health.

"The good news for smokers is that much of the added risk of a heart attack recedes after quitting - a great reason to kick the tobacco habit for good."